Surface aerator impeller design including stabilizer cylinder

ABSTRACT

A surface aeration impeller incorporating a stabilizer cylinder that damps out and eliminates any sustained oscillatory or vibratory displacements normal to the axis of rotation when the impeller is in operation. The surface aeration design operates in a mechanically stable fashion under diverse loading conditions and at any static liquid level submergence of the impeller.

RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.60/962,694, filed Jul. 31, 2007.

INTRODUCTION

The present teachings are directed to systems for achieving mechanicalstabilization in the operation of rotating surface aeration impellers.The present teachings are further directed to a stabilizer cylinderaffixed to a surface aeration impeller that damps out and eliminates anysustained oscillatory or vibratory displacements normal to the axis ofrotation when in operation under specific loading conditions.

Surface aeration is a well known approach for dissolution of gas intoliquid in gas-liquid contacting operations. Surface aeration uses animpeller located at or near the surface of the liquid to agitate, pumpand spray the liquid into the gas. A surface aerator system typicallycomprises an electric motor coupled to a speed reducing gear reducer,which is coupled to the surface aeration impeller by means of acylindrical shaft.

The discharge from the surface aerator has two flow components. Onecomponent is turbulent flow that is pumped along the liquid surface, andthe other is a stream that is discharged as a dense spray that impingeson the liquid surface at a distance from the surface aerator. Thecombination of the impinging spray and the turbulent surface flowresults in a region of dense turbulence downstream of the sprayimpingement point. This surface turbulence causes a large amount of gasbubbles to be entrained into the liquid surface. The surface turbulenceand the entrained gas produce high rates of gas dissolution into theliquid.

The HI-FLO II surface aerator design disclosed in U.S. Pat. Nos.6,715,912 and 6,860,631 has been shown to be a superior impeller designfor surface aeration purposes, with a substantial documented increase inliquid pumping and gas-liquid mass transfer efficiency over pre-existingart. The impeller designs disclosed therein pump more liquid per unit ofhorsepower input through the liquid spray mass transfer zone and intothe surrounding surface reaeration zone and thereby maximize the totalgas-liquid mass transfer efficiency of the overall surface aerationsystem.

Infrequently, under certain loading conditions, surface aerationimpellers may exhibit mechanically unstable performance characteristics.In such operating conditions, the surface aeration impeller may exhibita vibrating or oscillatory motion normal to the axis of rotation whichexerts very large mechanical bending forces on the impeller shaft. Theseforces may, in turn, be transmitted to the gear reducer. This can resultin excessive forces on the gearbox bearings and mechanical seals which,when excessive, cannot be tolerated even for short periods of operation.If not prevented, such forces for prolonged periods can cause mechanicaldamage and eventually mechanical failure in the system. Accordingly,there is a need to reduce the vibrating and/or oscillatory motion of theimpeller shaft, thereby minimizing the detrimental forces on the gearreducer, mechanical seal, etc.

Apparatus for reducing impeller shaft oscillatory motion are known inthe art. U.S. Pat. No. 6,089,748 discloses flexural members attached toan impeller shaft near the shaft's base; U.S. Pat. No. 5,931,051discloses a dampener using a liquid-filled housing. U.S. Pat. No.5,326,168 discloses the attachment of fins to the impeller blades toreduce such motion. However, using an oscillatory motion dampeningapparatus that is made up of multiple parts is both costly andburdensome. A further disadvantage of such apparatus is that it causesthe surface aeration impeller to be difficult to store when not in use.Therefore, there is a need for an apparatus that is capable ofeliminating any vibrating or irregular oscillatory motion of theimpeller shaft that is also inexpensive to produce, easy to use,durable, and easy to store.

SUMMARY

The present teachings disclose surface aeration impellers with improvedvibration and oscillatory motion dampening, stability and performance,for use in a liquid filled tank that has a free liquid surface and anenclosed or open gas space above the liquid surface in the tank. Theimproved surface aeration impeller design includes a stabilizingcylinder. The stabilizer cylinder can be positioned below the uppermounting member of the surface aeration impeller. The stabilizercylinder provides significantly increased resistance to vibration andirregular oscillatory motion in a direction that is perpendicular to theaxis of rotation. The stabilizer cylinder also dampens the effects ofthe fluid forces that cause the impeller shaft to vibrate and oscillate,and effectively eliminates both periodic and random motions of theimpeller shaft, thereby stabilizing the overall assembly and eliminatingthe unwanted forces on the gear reducer.

These and other features of the present teachings are set forth herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The skilled artisan will understand that the drawings described beloware for illustration purposes only. The drawings are not intended tolimit the scope of the present teachings in any way.

FIG. 1 is a perspective drawing of the surface aeration impeller withthe stabilizer cylinder attached to the underside of a disc-shapedmounting member.

FIG. 2 is a graph of the oxygen transfer efficiency of the presentteachings.

FIG. 3 is a series of illustrations depicting the present teachings fromdifferent perspectives. Impeller blades are shown with an endcap on thetrailing edge in accordance with the present teachings.

DESCRIPTION OF VARIOUS EMBODIMENTS

As described above, incorporating a stabilizer cylinder into the designof a surface aeration impeller essentially dampens and eliminates anytendency of the surface aeration impeller to exhibit unwantedvibrations, oscillatory motions or displacements normal to the axis ofrotation under any operating conditions and at any static liquid levelheight on the surface aeration impeller blades. Thus, the extensivebending forces on the impeller shaft and gearbox that occurinfrequently, but unpredictably, are completely eliminated or aregreatly reduced to have no negative impact on mechanical integrity. Thefact that this new surface aeration impeller design can operate in amechanically stable fashion at any static liquid level submergence ofthe impeller is unique in the industry. The stabilizer cylinder also hasthe unexpected and additional benefit of improving the gas-liquid masstransfer efficiency of surface aeration impellers, including the HI-FLOII aerator.

As referred to in this application, the term “stabilizer cylinder”refers to a substantially circular band of material that is positionedbeneath the surface aeration impeller's mounting member. As referred toin this application, the “mounting member” is the solid object to whichthe surface aerator impeller blades are attached. The mounting membercan be made of any rigid material (e.g., steel, plastic, aluminum,graphite composites) and is typically disc-shaped.

Referring to the Figures, there is shown in FIG. 1 a bottom perspectiveview of the improved surface aeration impeller 4 according to thepresent teachings. The surface aeration impeller 4 has a plurality ofvertically extending blades 2 affixed to the underside of the mountingmember 1. The blades 2 can be affixed to the mounting member 1 via anysemi-permanent or permanent means (e.g., bolting, welding). Thestabilizer cylinder 3 is positioned below the bottom surface of themounting member 1.

The stabilizer cylinder 3 can be constructed of any rigid material(e.g., steel, aluminum, plastic, graphite composites and polymercomposites). The type of stabilizer cylinder 3 material that is selectedwill depend on the type of liquid to be aerated by the surface aerationimpeller. For example, certain liquids may undergo an unwanted chemicalreaction when brought into contact with a steel stabilizer cylinder 3.

The stabilizer cylinder 3 can be any diameter compatible with theoverall diameter of the surface aerator impeller 4. The stabilizercylinder 3 diameter can be approximately less than or equal to theinterior diameter of the blades 2 or less than the exterior diameter ofthe blades 2. As used in this application, “interior diameter of theblades” refers to the diameter of the inwardly-facing vertical edges ofthe blades 2, and the phrase “exterior diameter of the blades” refers tothe diameter of the outwardly-facing vertical edges of the blades 2. Inaddition, the diameter of the stabilizer cylinder 3 can intersect thehorizontal surfaces of the blades 2. In some embodiments of the presentteachings, the diameter of the stabilizer cylinder 3 will depend on thenature of the liquid to be aerated and the type of aeration tank beingused. For example, a stabilizer cylinder 3 diameter that is greater thanthe exterior diameter of the blades 2 will provide the greatest amountof surface aerator impeller 4 stabilization. However, a stabilizercylinder 3 diameter that is greater than the exterior diameter of theblades 2 may reduce the efficiency of the surface aeration system bypreventing the liquid from coming into contact with the full surfacearea of the blades 2.

FIG. 3 illustrates various embodiments of the present teachings.Referring to FIG. 3, the stabilizer cylinder 3 can be connected to themounting member 1 by a plurality of rods 5, brackets, bolts, nuts, pinsor other available hardware that allows for firm attachment. Preferablythreaded rods 5, for example, can be constructed of any rigid materialsuch as steel or plastic. In some embodiments, the rods 5 can beattached to the stabilizer cylinder 3 via fasteners that are affixed tothe vertical surface of the stabilizer cylinder 3. The preferablythreaded fasteners can be standard hardware nuts that have been affixedto the stabilizer cylinder 3 in such a way as to cause threaded holes ofthe hardware nuts to face towards the bottom surface of the mountingmember 1. This arrangement allows for the stabilizer cylinder 3 to berepositioned along the rods 5, while also allowing complete removal ofthe rods 5 from the stabilizer cylinder 3 for ease of storage.

In various embodiments, the rods 5 can be permanently attached to thestabilizer cylinder 3 by welding or bolting them to the vertical surfaceof the stabilizer cylinder 3.

In some embodiments of the present teachings, and as shown in FIG. 3,the threaded rods 5 pierce the mounting member 1 and extend through theupper surface of the mounting member 1. A plurality of standard hex nutsand associated hardware can then be positioned along the threaded rods 5above and below the mounting member 1 to firmly hold the stabilizercylinder 3 below the mounting member 1. The hex nuts can be adjustedalong the length of the threaded rods 5 to raise or lower the stabilizercylinder 3 to the desired distance below the mounting member 1. It alsoenables the threaded rods 5 to be removed from the mounting member 1 foreasy storage. In some embodiments, the threaded rods 5 are permanentlyattached (e.g., welded, riveted) to the bottom surface of the mountingmember 1, extending downward therefrom.

The stabilizer cylinder 3 can be positioned up against the bottomsurface of the mounting member 1, as shown in FIG. 1. In variousembodiments, the stabilizer cylinder 3 can be positioned below themounting member 2 so that it does not come into contact with themounting member 1, as shown in FIG. 3. The location of the stabilizercylinder 3 that is selected will depend on the nature of the liquidbeing aerated and the type of aeration tank being used. The further awayfrom the mounting member 1 the stabilizer cylinder 3 is positioned, thegreater the stabilization of the surface aeration impeller 4. However,positioning the stabilizer cylinder 3 further down into the liquid beingaerated increases the risk of the stabilizer cylinder 3 encounteringmaterial known in the industry as “rags,” and other stringy materialsthat can become entangled in the surface aeration impeller 4 and reduceits performance. As used herein, the term “rags” generally refers tosolid and semi-solid materials that are present in certain liquidsundergoing aeration (especially wastewater in treatment plants).

In various embodiments of the present teachings, the space between theinside vertical edge of the blade 1 and the stabilizing cylinder 3 isfilled in with metal. In some embodiments, the outer tip of the blade 1is trimmed with an angled cut, thereby eliminating the usual point ofcontact that occurs at such outer tip. The stabilizer ring 3 can also bedirectly welded to the inside vertical edge of the blades 1, avoidingthe need to suspend the ring 3 from mounting member 1. In theseembodiments, the possibility of “rags” getting entangled in thesupporting rods is eliminated.

The stabilizer cylinder 3 can be of varying heights that are compatibleoverall with the diameter of the surface aeration impeller 4.Determinations relative to height may take into account the nature ofthe liquid being aerated and the type of aeration tank being used. Ageneral principle is that the greater the height of the stabilizercylinder 3, the greater the stabilization of the surface aerationimpeller 4. Referring to FIG. 2, the stabilizer cylinder 3 also providesan improvement in the oxygen mass transfer efficiency of the surfaceaeration impeller 4 as shown in the graph of FIG. 2.

The blades 2 of the present teachings have an optional additionalsegment known as an endcap. The endcap 6 is shown, for example, in FIG.3. The endcap is a relatively flat geometric piece positionedessentially perpendicular to a vertical section 7 of the blade andconnects the outer or trailing edges of both the vertical section 8 anda lower section 7 of the blade. While the exact shape of the endcap canvary widely, the critical feature of the endcap 6 is that it preventsliquid from flowing or “sliding” off the trailing edge of the blades 2below the vertical section 8 and simultaneously enhances the upliftingor up-pumping capability of the surface aeration impeller 4. Theinventors have found that an endcap 6 can significantly increase thepower delivered, and simultaneously increase the standard aerationefficiency.

The section headings used herein are for organizational purposes onlyand are not to be construed as limiting the subject matter described inany way.

While the present teachings are described in conjunction with variousembodiments, it is not intended that the present teachings be limited tosuch embodiments. On the contrary, the present teachings encompassvarious alternatives, modifications, and equivalents, as will beappreciated by those of skill in the art.

1. A surface aeration impeller designed to rotate about an axisperpendicular to a liquid surface, said impeller comprising: (a) aplurality of blades attached to a mounting member wherein said bladeseach have an inside vertical edge forming an interior diameter and anoutside vertical edge forming an exterior diameter; (b) said mountingmember having a top surface and a bottom surface; and (c) a stabilizercylinder positioned below the bottom surface of said mounting member. 2.A surface aeration impeller designed to rotate about an axisperpendicular to a liquid surface, said impeller comprising: (a) aplurality of blades attached to a mounting member wherein said bladeseach have an inside vertical edge forming an interior diameter and anoutside vertical edge forming an exterior diameter; (b) said mountingmember having a top surface and a bottom surface; and (c) a stabilizercylinder positioned below the bottom surface of said mounting member,said stabilizer cylinder being physically attached to the bottom surfaceof said mounting member.
 3. The surface aeration impeller according toclaim 1 or 2, further comprising: a plurality of essentially verticalblades attached to the underside of a horizontal mounting member whereinsaid blades each have an inside vertical edge forming an interiordiameter and an outside vertical edge forming an exterior diameter. 4.The surface aeration impeller according to claim 1 or 2, wherein saidblades additionally contain an endcap.
 5. The surface aeration impelleraccording to claim 1 or 2, wherein the diameter of said stabilizercylinder is less than or equal to the interior diameter of said blades.6. The surface aeration impeller according to claim 1 or 2, wherein thediameter of said stabilizer cylinder is greater than or equal to theexterior diameter of said blades.
 7. The surface aeration impelleraccording to claim 1 or 2, wherein the height of said stabilizercylinder is less than the height of said blades.
 8. The surface aerationimpeller according to claim 1 or 2, wherein the height of saidstabilizer cylinder is greater than the height of said blades.
 9. Thesurface aeration impeller according to claim 1 or 2, wherein the heightof said stabilizer cylinder is equal to the height of said blades. 10.The surface aeration impeller according to claim 1 or 2, wherein saidstabilizer cylinder is attached to the mounting member with threadedrods and fasteners.
 11. The surface aeration impeller according to claim1 or 2, wherein said stabilizer cylinder is smaller than the interiordiameter of said blades, and the outer surface of said stabilizercylinder is directly attached to the inside vertical edge of each blade.12. The surface aeration impeller according to claim 1 or 2, wherein thediameter of said stabilizer cylinder intersects the horizontal surfaceof said blades.
 13. The surface aeration impeller according to claim 1or 2, wherein said stabilizer cylinder is directly attached to the axisperpendicular to said liquid surface.